One of my biggest hurdles is creating apps for each target ( Desktop, Web, and iOS ) without having to essentially rewrite the app three times. I don’t mind a bit of extra code for each platform, but it should be the exception.
Are there any controls that work across all targets? Desktop Listbox, Web Listbox, and iOS Listbox are incredibly different on each for example. This makes sharing code between targets very difficult.
I really like how Web Apps can be run on ANY target via a browser. It just works.
I experimented a while back and created a Web App and then placed it in a Mac App’s Package. When the Mac App launched, it started the Web App which I could interact with the Mac App’s HTMLViewer. I don’t think I could ever get that approved on the Mac App Store though. 
I’m certain this would work for a Windows App. Probably not possible for an iOS app.
How are you making development easier across platforms?